Catalytic fuel tank inerting apparatus for aircraft

ABSTRACT

Fuel tank inerting systems for aircraft are described. The systems include a fuel tank, a first reactant source fluidly connected to the fuel tank, a second reactant source, a catalytic reactor arranged to receive a first reactant from the first source and a second reactant from the second source to generate an inert gas that is supplied to the fuel tank to fill a ullage space of the fuel tank, a heat exchanger arranged between the catalytic reactor and the fuel tank and configured to at least one of cool and condense an output from the catalytic reactor to separate out an inert gas and a byproduct, a reheater arranged between the catalytic reactor and the heat exchanger, and a recirculation loop configured to extract air from downstream of the heat exchanger, pass the extracted air through the reheater, and inject reheated air upstream of the catalytic reactor.

BACKGROUND

The subject matter disclosed herein generally relates to fuel tankinerting systems for aircraft and, more particularly, to fuel tankinerting systems configured to supply inert gas in an aircraft.

In general, aircraft pneumatic systems including, air conditioningsystems, cabin pressurization and cooling, and fuel tank inertingsystems are powered by engine bleed air. For example, pressurized airfrom an engine of the aircraft is provided to a cabin through a seriesof systems that alter the temperatures and pressures of the pressurizedair. To power this preparation of the pressurized air, generally thesource of energy is the pressure of the air itself.

The air bled from engines may be used for environmental control systems,such as used to supply air to the cabin and to other systems within anaircraft. Additionally, the air bled from engines may be supplied toinerting apparatuses to provide inert gas to a fuel tank. In othercases, the air may be sourced from compressed RAM air.

Regardless of the source, typically the air for fuel tank inerting ispassed through a porous hollow fiber membrane tube bundle known as an“air separation module.” A downstream flow control valve is controlledor passively operated to apply back pressure on the air separationmodule to force some amount of air through the membrane as opposed toflowing though the tube. Oxygen passes more easily through the membrane,leaving only nitrogen enriched air to continue through the flow controlvalve into the fuel tank. Typically air separation modules employ adedicated ram air heat exchanger in conjunction with a bypass valve.

BRIEF DESCRIPTION

According to some embodiments, fuel tank inerting systems for aircraftare provided. The systems include a fuel tank, a first reactant sourcefluidly connected to the fuel tank, the first source arranged to receivefuel from the fuel tank, a second reactant source, a catalytic reactorarranged to receive a first reactant from the first source and a secondreactant from the second source to generate an inert gas that issupplied to the fuel tank to fill a ullage space of the fuel tank, aheat exchanger arranged between the catalytic reactor and the fuel tankand configured to at least one of cool and condense an output from thecatalytic reactor to separate out an inert gas and a byproduct, areheater arranged between the catalytic reactor and the heat exchanger,and a recirculation loop configured to extract air from downstream ofthe heat exchanger, pass the extracted air through the reheater, andinject reheated air upstream of the catalytic reactor.

In addition to one or more of the features described above, or as analternative, further embodiments of the fuel tank inerting systems mayinclude a recirculation fan located within the recirculation loop, therecirculation fan configured to pull air from downstream of the heatexchanger.

In addition to one or more of the features described above, or as analternative, further embodiments of the fuel tank inerting systems mayinclude that the recirculation fan is an electric motor-driven fan.

In addition to one or more of the features described above, or as analternative, further embodiments of the fuel tank inerting systems mayinclude that the recirculation loop fluidly connects to the heatexchanger at a hot corner tap of the heat exchanger.

In addition to one or more of the features described above, or as analternative, further embodiments of the fuel tank inerting systems mayinclude that the recirculation loop fluidly connects downstream of theheat exchanger at a recirculation junction.

In addition to one or more of the features described above, or as analternative, further embodiments of the fuel tank inerting systems mayinclude that the heat exchanger comprises a recirculation heat exchangerand a condenser heat exchanger, wherein output from the catalyticreactor passes through the reheater and into the recirculation heatexchanger and is subsequently divided to the recirculation loop and thecondenser heat exchanger.

In addition to one or more of the features described above, or as analternative, further embodiments of the fuel tank inerting systems mayinclude a water separator located between the catalytic reactor and thefuel tank and downstream of the catalytic reactor, the water separatorarranged to extract water from the reacted first reactant and secondreactant.

In addition to one or more of the features described above, or as analternative, further embodiments of the fuel tank inerting systems mayinclude an injector pump arranged to receive the first reactant and thesecond reactant and to supply a mixture of the first reactant and thesecond reactant to the catalytic reactor.

In addition to one or more of the features described above, or as analternative, further embodiments of the fuel tank inerting systems mayinclude a fuel pump configured to pump fuel from the fuel tank to thecatalytic reactor.

In addition to one or more of the features described above, or as analternative, further embodiments of the fuel tank inerting systems mayinclude that the byproduct is water.

According to some embodiments, methods for supplying inert gas to fueltanks of aircraft are provided. The methods include extracting fuel froma fuel tank as a first reactant source, mixing the first reactant with asecond reactant supplied from a second reactant source, catalyzing themixed first reactant and second reactant within a catalytic reactor,cooling the catalyzed mixture of the first and second reactants with aheat exchanger to produce an inert gas, supplying the inert gas to thefuel tank to fill a ullage space of the fuel tank, and recirculating andreheating, through a recirculation loop, a portion of the reacted firstand second reactants and supplying the recirculated portion to alocation upstream of the catalytic reactor, wherein a reheater islocated between the catalytic reactor and the heat exchanger.

In addition to one or more of the features described above, or as analternative, further embodiments of the methods may include pulling airfrom downstream of the heat exchanger using a recirculation fan locatedwithin the recirculation loop.

In addition to one or more of the features described above, or as analternative, further embodiments of the methods may include that therecirculation fan is an electric motor-driven fan.

In addition to one or more of the features described above, or as analternative, further embodiments of the methods may include that therecirculation loop fluidly connects to the heat exchanger at a hotcorner tap of the heat exchanger.

In addition to one or more of the features described above, or as analternative, further embodiments of the methods may include that therecirculation loop fluidly connects downstream of the heat exchanger ata recirculation junction.

In addition to one or more of the features described above, or as analternative, further embodiments of the methods may include that theheat exchanger comprises a recirculation heat exchanger and a condenserheat exchanger, wherein output from the catalytic reactor passes throughthe reheater and into the recirculation heat exchanger and issubsequently divided to the recirculation loop and the condenser heatexchanger.

In addition to one or more of the features described above, or as analternative, further embodiments of the methods may include extractingwater from the reacted first reactant and second reactant using a waterseparator located between the catalytic reactor and the fuel tank anddownstream of the catalytic reactor.

In addition to one or more of the features described above, or as analternative, further embodiments of the methods may include mixing thefirst reactant and the second reactant using an injector pump andsupplying the mixed first reactant and second reactant to the catalyticreactor.

In addition to one or more of the features described above, or as analternative, further embodiments of the methods may include pumping fuelfrom the fuel tank to the catalytic reactor using a fuel pump.

In addition to one or more of the features described above, or as analternative, further embodiments of the methods may include that theextracted portion downstream of the heat exchanger and within therecirculation loop is between 60° F. and 200° F.

The foregoing features and elements may be combined in variouscombinations without exclusivity, unless expressly indicated otherwise.These features and elements as well as the operation thereof will becomemore apparent in light of the following description and the accompanyingdrawings. It should be understood, however, that the followingdescription and drawings are intended to be illustrative and explanatoryin nature and non-limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1A is a schematic illustration of an aircraft that can incorporatevarious embodiments of the present disclosure;

FIG. 1B is a schematic illustration of a bay section of the aircraft ofFIG. 1A;

FIG. 2 is a schematic illustration of a fuel tank inerting system inaccordance with an embodiment of the present disclosure;

FIG. 3 is a schematic illustration of a fuel tank inerting system inaccordance with an embodiment of the present disclosure;

FIG. 4 is a schematic illustration of a fuel tank inerting system inaccordance with an embodiment of the present disclosure;

FIG. 5 is a schematic illustration of a fuel tank inerting system inaccordance with an embodiment of the present disclosure;

FIG. 6A is a schematic illustration of a fuel tank inerting system inaccordance with an embodiment of the present disclosure;

FIG. 6B is a schematic illustration of a portion of the fuel tankinerting system of FIG. 6A;

FIG. 7 is a schematic illustration of a fuel tank inerting system inaccordance with an embodiment of the present disclosure;

FIG. 8 is a schematic illustration of a fuel tank inerting system inaccordance with an embodiment of the present disclosure;

FIG. 9 is a schematic illustration of a fuel tank inerting system inaccordance with an embodiment of the present disclosure;

FIG. 10 is a schematic illustration of a fuel tank inerting system inaccordance with an embodiment of the present disclosure;

FIG. 11 is a schematic illustration of a fuel tank inerting system inaccordance with an embodiment of the present disclosure;

FIG. 12 is a schematic illustration of a fuel tank inerting system inaccordance with an embodiment of the present disclosure;

FIG. 13 is a schematic illustration of a fuel tank inerting system inaccordance with an embodiment of the present disclosure;

FIG. 14 is a schematic illustration of a fuel tank inerting system inaccordance with an embodiment of the present disclosure;

FIG. 15 is a schematic illustration of a fuel tank inerting system inaccordance with an embodiment of the present disclosure;

FIG. 16 is a schematic illustration of a fuel tank inerting system inaccordance with an embodiment of the present disclosure; and

FIG. 17 is a schematic illustration of a fuel tank inerting system inaccordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION

FIGS. 1A-1B are schematic illustrations of an aircraft 101 that canemploy one or more embodiments of the present disclosure. As shown inFIGS. 1A-1B, the aircraft 101 includes bays 103 beneath a center wingbox. The bays 103 can contain and/or support one or more components ofthe aircraft 101. For example, in some configurations, the aircraft 101can include environmental control systems and/or fuel inerting systemswithin the bay 103. As shown in FIG. 1B, the bay 103 includes bay doors105 that enable installation and access to one or more components (e.g.,environmental control systems, fuel inerting systems, etc.). Duringoperation of environmental control systems and/or fuel inerting systemsof the aircraft 101, air that is external to the aircraft 101 can flowinto one or more environmental control systems within the bay doors 105through one or more ram air inlets 107. The air may then flow throughthe environmental control systems to be processed and supplied tovarious components or locations within the aircraft 101 (e.g., passengercabin, fuel inerting systems, etc.). Some air may be exhaust through oneor more ram air exhaust outlets 109.

Also shown in FIG. 1A, the aircraft 101 includes one or more engines111. The engines 111 are typically mounted on wings of the aircraft 101,but may be located at other locations depending on the specific aircraftconfiguration. In some aircraft configurations, air can be bled from theengines 111 and supplied to environmental control systems and/or fuelinerting systems, as will be appreciated by those of skill in the art.

As noted above, typical air separation modules operate using pressuredifferentials to achieve desired air separation. Such systems require ahigh pressure pneumatic source to drive the separation process acrossthe membrane. Further, the hollow fiber membrane separators commonlyused are relatively large in size and weight, which is a significantconsideration with respect to aircraft (e.g., reductions in volume andweight of components can improve flight efficiencies). Embodimentsprovided herein provide reduced volume and/or weight characteristics ofinert-gas or low-oxygen supply systems for aircraft. Further,embodiments provided herein can prevent humid air from entering fueltanks of the aircraft, thus preventing various problems that may arisewith some fuel system components. In accordance with some embodiments ofthe present disclosure, the typical hollow fiber membrane separator isreplaced by a catalytic system (e.g., CO₂ generation system), which canbe, for example, smaller, lighter, and/or more efficient than thetypical fiber membrane separators. That is, in accordance withembodiments of the present disclosure, the use of hollow fiber membraneseparators may be eliminated.

A function of fuel tank flammability reduction systems in accordancewith embodiments of the present disclosure is accomplished by reacting asmall amount of fuel vapor (e.g., a “first reactant”) with a source ofgas containing oxygen (e.g., a “second reactant”). The product of thereaction is carbon dioxide and water vapor. The source of the secondreactant (e.g., air) can be bleed air or any other source of aircontaining oxygen, including, but not limited to, high-pressure sources(e.g., engine), bleed air, cabin air, etc. A catalyst material is usedto induce a chemical reaction, including, but not limited to, preciousmetal materials. The carbon dioxide that results from the reaction is aninert gas that is mixed with nitrogen naturally found in fresh/ambientair, and is directed back within a fuel tank to create an inertenvironment within the fuel tank, thus reducing a flammability of thevapors in the fuel tank. Further, in some embodiments, the fuel tankflammability reduction or inerting systems of the present disclosure canprovide a functionality such that water vapor from the atmosphere doesnot enter the fuel tanks during descent stages of flight of an aircraft.This can be accomplished by controlling a flow rate of inert gas intothe fuel tank so that a positive pressure is continuously maintained inthe fuel tank.

In accordance with embodiments of the present disclosure, a catalyst isused to induce a chemical reaction between oxygen (O₂) and fuel vapor toproduce carbon dioxide (CO₂) and water vapor. The source of O₂ used inthe reaction can come from any of a number of sources, including, butnot limited to, pneumatic sources on an aircraft that supply air at apressure greater than ambient. The fuel vapor is created by draining asmall amount of fuel from an aircraft fuel tank into an evaporatorcontainer. The fuel can be heated to vaporize the fuel, such as by usingan electric heater, as shown and described in some embodiments of thepresent disclosure. The fuel vapor is removed from the evaporatorcontainer, in some embodiments, by an ejector which can induce a suctionpressure that pulls the fuel vapor out of the evaporator container. Suchejectors can utilize elevated pressures of a second reactant sourcecontaining O₂ (e.g., a pneumatic source) to induce a secondary flow ofthe ejector which is sourced from the evaporator container. As such, theejector can be used to mix the extracted fuel vapor with the O₂ from asecond reactant source.

The mixed air stream (fuel vapor and Oxygen or air) is then introducedto a catalyst, which induces a chemical reaction that transforms the O₂and fuel vapor into CO₂ and water vapor. Any inert gas species that arepresent in the mixed stream (for example, Nitrogen), will not react andwill thus pass through the catalyst unchanged. In some embodiments, thecatalyst is in a form factor that acts as a heat exchanger. For example,in one non-limiting configuration, a plate fin heat exchangerconfiguration is employed wherein a hot side of the heat exchanger wouldbe coated with catalyst material. In such arrangement, the cold side ofthe catalyst heat exchanger can be fed with a cool air source, such asram air or some other source of cold air. The air through the cold sideof the heat exchanger can be controlled such that the temperature of ahot, mixed-gas stream is hot enough to sustain a desired chemicalreaction within or at the catalyst. Further, the cooling air can be usedto maintain a cool enough temperature to enable removal of heatgenerated by exothermic reactions at the catalyst.

As noted above, the catalytic chemical reaction generates water vapor.Having water (in any form) enter primary fuel tank can be undesirable.Thus, in accordance with embodiments of the present disclosure, thewater from a product gas stream (e.g., exiting the catalyst) can beremoved through various mechanisms, including, but not limited to,condensation. The product gas stream can be directed to enter a heatexchanger downstream from the catalyst that is used to cool the productgas stream such that the water vapor condenses and drops out of theproduct gas stream. The liquid water can then be drained overboard. Insome embodiments, an optional water separator can be used to augment orprovide water separation from the product stream.

In some embodiments, a flow control valve meters a flow of an inert gas(with water vapor removed therefrom) to a predetermined and/orcontrolled inert gas flow rate. Further, in some embodiments, anoptional fan can be used to boost the inert gas stream pressure toovercome a pressure drop associated with ducting and flow lines betweenthe catalyst and a fuel tank into which the inert gas is supplied. Insome embodiments, a flame arrestor can be arranged at an inlet to thefuel tank (where the inert gas enters) to prevent any potential flamesfrom propagating into the fuel tank.

Independent of any aircraft flammability reduction systems, aircraftfuel tanks are typically vented to ambient. At altitude, pressure insidethe fuel tank is very low and is roughly equal to ambient pressure.However, during descent, the pressure inside the fuel tank needs to riseto equal ambient pressure at sea level (or at whatever altitude theaircraft is landing). The change in pressures requires gas entering thetank from outside to equalize the pressure. When air from outside entersthe tank, water vapor is normally present with it. Water can becometrapped in the fuel tank and cause problems. In accordance withembodiments of the present disclosure, to prevent water from enteringthe fuel tanks, the fuel inerting systems of the present disclosure canrepressurize the fuel tanks with dry inert gas that is generated asdescribed above and below. The repressurization can be accomplished byusing a flow control valve to control the flow of inert gas into thefuel tank such that a positive pressure is constantly maintained in thefuel tank. The positive pressure within the fuel tank can prevent airfrom entering the fuel tank from outside during descent and thereforeprevent water from entering the fuel tank.

FIG. 2 is a schematic illustration of a flammability reduction orinerting system 200 utilizing a catalytic reaction to produce inert gasin accordance with an embodiment of the present disclosure. The inertingsystem 200, as shown, includes a fuel tank 202 having fuel 204 therein.As the fuel 204 is consumed during operation of one or more engines, anullage space 206 forms within the fuel tank 202. To reduce flammabilityrisks associated with vaporized fuel that may form within the ullagespace 206, an inert gas can be generated and fed into the ullage space206.

In accordance with embodiments of the present disclosure, an inertingfuel 208 can be extracted from the fuel tank 202 and into an evaporatorcontainer 210. The amount of fuel 204 that is extracted into theevaporator container 210 (i.e., the amount of inerting fuel 208) can becontrolled by an evaporator container valve 212, such as a float valve.The inerting fuel 208, which may be in liquid form when pulled from thefuel tank 202, can be vaporized within the evaporator container 210using a heater 214, such as an electric heater, to generate a firstreactant 216. The first reactant 216 is a vaporized portion of theinerting fuel 208 located within the evaporator container 210. The firstreactant 216 is mixed with a second reactant 218 which is sourced from asecond reactant source 220. The second reactant 218 is air containingoxygen that is catalyzed with the first reactant 216 to generate aninert gas to be supplied into the ullage space 206 of the fuel tank 202.The second reactant 218 can come from any source on an aircraft that isat a pressure greater than ambient, including, but not limited to bleedair from an engine, cabin air, high pressure air extracted or bled froman engine, etc. (i.e., any second reactant source 220 can take anynumber of configurations and/or arrangements). The first reactant 216within the evaporator container 210 and the second reactant 218 can bedirected into a catalytic reactor 222 by and/or through a mixer 224,which, in some embodiments, may be an ejector or jet pump. The mixer 224will mix the first and second reactants 216, 218 into a mixed air stream225.

The catalyst 222 can be temperature controlled to ensure a desiredchemical reaction efficiency such that an inert gas can be efficientlyproduced by the inerting system 200 from the mixed air stream 225.Accordingly, cooling air 226 can be provided to extract heat from thecatalytic reactor 222 to achieve a desired thermal condition for thechemical reaction within the catalytic reactor 222. The cooling air 226can be sourced from a cool air source 228. A catalyzed mixture 230leaves the catalytic reactor 222 and is passed through a heat exchanger232. The heat exchanger 232 operates as a condenser on the catalyzedmixture 230 to separate out an inert gas 234 and a byproduct 236. Acooling air is supplied into the heat exchanger 232 to achieve thecondensing functionality. In some embodiments, as shown, a cooling air226 can be sourced from the same cool air source 228 as that provided tothe catalytic reactor 222, although in other embodiments the cool airsources for the two components may be different. The byproduct 236 maybe liquid water or water vapor, and thus in the present configurationshown in FIG. 2, a water separator 238 is provided downstream of theheat exchanger 232 to extract the liquid water or water vapor from thecatalyzed mixture 230, thus leaving only the inert gas 234 to beprovided to the ullage space 206 of the fuel tank 202.

The inerting system 200 can include additional components including, butnot limited to, a fan 240, a flame arrestor 242, and a controller 244.Various other components can be included without departing from thescope of the present disclosure. Further, in some embodiments, certainof the included components may be optional and/or eliminated. Forexample, in some arrangements, the fan 240 and/or the water separator238 can be omitted. The controller 244 can be in operable communicationwith one or more sensors 246 and valves 248 to enable control of theinerting system 200.

In one non-limiting example, flammability reduction is achieved by theinerting system 200 by utilizing the catalytic reactor 222 to induce achemical reaction between oxygen (second reactant 218) and fuel vapor(first reactant 216) to produce carbon dioxide (inert gas 234) and waterin vapor phase (byproduct 236). The source of the second reactant 218(e.g., oxygen) used in the reaction can come from any source on theaircraft that is at a pressure greater than ambient. The fuel vapor(first reactant 216) is created by draining a small amount of fuel 204from the fuel tank 202 (e.g., a primary aircraft fuel tank) into theevaporator container 210. The inerting fuel 208 within the evaporatorcontainer 210 is heated using the electric heater 214. In someembodiments, the first reactant 216 (e.g., fuel vapor) is removed fromthe evaporator container 210 by using the mixer 224 to induce a suctionpressure that pulls the first reactant 216 out of the evaporatorcontainer 210. The mixer 224, in such embodiments, utilizes the elevatedpressure of the second reactant source 220 to induce a secondary flowwithin the mixer 224 which is sourced from the evaporator container 210.Further, as noted above, the mixer 224 is used to mix the two gasstreams (first and second reactants 216, 218) together to form the mixedair stream 225.

The mixed air stream 225 (e.g., fuel vapor and oxygen or air) is thenintroduced to the catalytic reactor 222, inducing a chemical reactionthat transforms the mixed air stream 225 (e.g., fuel and air) into theinert gas 234 and the byproduct 236 (e.g., carbon dioxide and watervapor). It is noted that any inert gas species that are present in themixed air stream 225 (for example, nitrogen) will not react and willthus pass through the catalytic reactor 222 unchanged. In someembodiments, the catalytic reactor 222 is in a form factor that acts asa heat exchanger. For example, one non-limiting configuration may be aplate fin heat exchanger wherein the hot side of the heat exchangerwould be coated with the catalyst material. Those of skill in the artwill appreciate that various types and/or configurations of heatexchangers may be employed without departing from the scope of thepresent disclosure. The cold side of the catalyst heat exchanger can befed with the cooling air 226 from the cool air source 228 (e.g., ram airor some other source of cold air). The air through the cold side of thecatalyst heat exchanger can be controlled such that the temperature ofthe hot mixed gas stream 225 is hot enough to sustain the chemicalreaction desired within the catalytic reactor 222, but cool enough toremove the heat generated by the exothermic reaction, thus maintainingaircraft safety and materials from exceeding maximum temperature limits.

As noted above, the chemical reaction process within the catalyticreactor 222 can produce byproducts, including water in vapor form. Itmay be undesirable to have water (in any form) enter the fuel tank 202.Accordingly, water byproduct 236 can be removed from the product gasstream (i.e., inert gas 234) through condensation. To achieve this,catalyzed mixture 230 enters the heat exchanger 232 that is used to coolthe catalyzed mixture 230 such that the byproduct 236 can be removed(e.g., a majority of the water vapor condenses and drops out of thecatalyzed mixture 230). The byproduct 236 (e.g., liquid water) can thenbe drained overboard. An optional water separator 238 can be used toaccomplish this function.

A flow control valve 248 located downstream of the heat exchanger 232and optional water separator 238 can meter the flow of the inert gas 234to a desired flow rate. An optional boost fan 240 can be used to boostthe gas stream pressure of the inert gas 234 to overcome a pressure dropassociated with ducting between the outlet of the heat exchanger 232 andthe discharge of the inert gas 234 into the fuel tank 202. The flamearrestor 242 at an inlet to the fuel tank 202 is arranged to prevent anypotential flames from propagating into the fuel tank 202.

Typically, independent of any aircraft flammability reduction system(s),aircraft fuel tanks (e.g., fuel tank 202) need to be vented to ambient.Thus, as shown in FIG. 2, the fuel tank 202 includes a vent 250. Ataltitude, pressure inside the fuel tank 202 is very low and is roughlyequal to ambient pressure. During descent, however, the pressure insidethe fuel tank 202 needs to rise to equal ambient pressure at sea level(or whatever altitude the aircraft is landing at). This requires gasentering the fuel tank 202 from outside to equalize the pressure. Whenair from outside enters the fuel tank 202, water vapor can be carried bythe ambient air into the fuel tank 202. To prevent water/water vaporfrom entering the fuel tank 202, the inerting system 200 canrepressurize the fuel tank 202 with the inert gas 234 generated by theinerting system 200. This is accomplished by using the valves 248. Forexample, one of the valves 248 may be a flow control valve 252 that isarranged fluidly downstream from the catalytic reactor 222. The flowcontrol valve 252 can be used to control the flow of inert gas 234 intothe fuel tank 202 such that a slightly positive pressure is alwaysmaintained in the fuel tank 202. Such positive pressure can preventambient air from entering the fuel tank 202 from outside during descentand therefore prevent water from entering the fuel tank 202.

As noted above, the controller 244 can be operably connected to thevarious components of the inerting system 200, including, but notlimited to, the valves 248 and the sensors 246. The controller 244 canbe configured to receive input from the sensors 246 to control thevalves 248 and thus maintain appropriate levels of inert gas 234 withinthe ullage space 206. Further, the controller 244 can be arranged toensure an appropriate amount of pressure within the fuel tank 202 suchthat, during a descent of an aircraft, ambient air does not enter theullage space 206 of the fuel tank 202.

In some embodiments, the inerting system 200 can supply inert gas tomultiple fuel tanks on an aircraft. As shown in the embodiment of FIG.2, an inerting supply line 254 fluidly connects the fuel tank 202 to theevaporator container 210. After the inert gas 234 is generated, theinert gas 234 will flow through a fuel tank supply line 256 to supplythe inert gas 234 to the fuel tank 202 and, optionally, additional fueltanks 258, as schematically shown.

Turning now to FIG. 3, an embodiment of an inerting system 300 inaccordance with the present disclosure is shown. The inerting system 300may be similar to that shown and described above, and thus similarfeatures may not be shown or discussed for simplicity. The inertingsystem 300 enables the elimination of the heater that is used tovaporize the inerting fuel that is within an evaporator container.

As shown, the inerting system 300 includes a fuel tank 302 having fuel304 therein, with an ullage space 306 formed as fuel 304 is consumedduring use. An inerting supply line 354 fluidly connects the fuel tank302 to an evaporator container 310, as described above. The amount offuel 304 that is extracted into the evaporator container 310 (i.e., theamount of inerting fuel 308) can be controlled by an evaporatorcontainer valve 312, such as a float valve, and/or operation and/orcontrol by a controller 344. The inerting fuel 308 is vaporized togenerate a first reactant 316 for use within a catalytic reactor 322. Asecond reactant can be sourced from a second reactant source 320, asdescribed above. The first and second reactants are reacted within thecatalytic reactor 322 to generate an inert gas for supply into one ormore fuel tanks (e.g., fuel tank 302).

In this embodiment, a cool air source 328, such as ram air, is providedto enable cooling of the catalytic reactor 322 as well as enable acondensing function within a heat exchanger 332, as described above. Theheat exchanger 332 operates as a condenser on a catalyzed mixture toseparate out an inert gas and a byproduct, as described above. In thisembodiment, the cooling air is sourced from the same cool air source 328as that provided to the catalytic reactor 322.

To provide thermal energy for evaporation of the inerting fuel 308,rather than employing a heater element or device, the thermal energy canbe supplied from the catalytic reactor 322. That is, heated air 360generated by exothermic reactions at the catalytic reactor 322 can bedirected into and/or through the evaporator container 310 through aheating duct 362. The heating duct 362 can pass through an interior ofthe evaporator container 310, may be wrapped around the evaporatorcontainer 310, and/or may have another arrangement such that thermalenergy within the heated air 360 can be transferred into the inertingfuel 308 to thus vaporize the inerting fuel 308. Advantageously, suchconfiguration can reduce weight of the system by eliminating the heatershown in FIG. 2.

Various embodiments provided herein are directed to elimination of theheater (e.g., heater 214 shown in FIG. 2). One arrangement is that shownin FIG. 3, using excess heat from the catalytic reactor. In otherembodiments, as described below, direct injection of fuel from the fueltank can be employed. Accordingly, such systems, such as that shown inFIGS. 4-7, can employ direct injection systems having variousconfigurations. In such embodiments, the typical heater is eliminatedand the first reactant is sourced directly from the fuel tank or theevaporator container.

Turning now to FIG. 4, an embodiment of an inerting system 400 inaccordance with the present disclosure is shown. The inerting system 400may be similar to that shown and described above, and thus similarfeatures may not be shown or discussed for simplicity. The inertingsystem 400 enables the elimination of the heater that is used tovaporize the inerting fuel that is within an evaporator container.

As shown, the inerting system 400 includes a fuel tank 402 having fuel404 therein, with an ullage space 406 formed as fuel 404 is consumedduring use. An inerting supply line 454 fluidly connects the fuel tank402 to an evaporator container 410, as described above. The amount offuel 404 that is extracted into the evaporator container 410 (i.e., theamount of inerting fuel 408) can be controlled by an evaporatorcontainer valve 412, such as a float valve, and/or operation and/orcontrol by a controller 444. Rather than vaporizing the inerting fuel408 prior to supplying it into a catalytic reactor 422, a portion of theinerting fuel 408 within the evaporator tank container 410 can beextracted in liquid form and then injected into an air stream where itis vaporized. In one such embodiment, as shown in FIG. 4, a gravitysupply line 464 can fluidly connect the evaporator container 410 to asupply line of a second reactant source 420 supply line, asschematically shown. As the inerting fuel 408 enters the supply line,the fuel vaporizes to generate a first reactant. The first and secondreactants are reacted within the catalytic reactor 422 to generate aninert gas for supply into one or more fuel tanks (e.g., fuel tank 402).Similar to the prior embodiment, a cool air source 428, such as ram air,is provided to enable cooling of the catalytic reactor 422 as well asenable a condensing function within a heat exchanger 432, as describedabove. The heat exchanger 432 operates as a condenser on a catalyzedmixture to separate out an inert gas and a byproduct, as describedabove. In this embodiment, the cooling air is sourced from the same coolair source 428 as that provided to the catalytic reactor 422. Becausethe inerting fuel 408 is gravity fed into the supply line of the secondreactant 420 and vaporized therein, there is no need for a heater to beinstalled within or to the evaporator container 410. That is, theinerting fuel 408 is directly injected into the second reactant togenerate the composition to be reacted within the catalytic reactor 422.

Turning now to FIG. 5, an embodiment of an inerting system 500 inaccordance with the present disclosure is shown. The inerting system 500may be similar to that shown and described above, and thus similarfeatures may not be shown or discussed for simplicity. The inertingsystem 500 enables the elimination of the heater that is used tovaporize the inerting fuel that is within an evaporator container.

As shown, the inerting system 500 includes a fuel tank 502 having fuel504 therein, with an ullage space 506 formed as fuel 504 is consumedduring use. An inerting supply line 554 fluidly connects the fuel tank502 to an evaporator container 510, as described above. The amount offuel 504 that is extracted into the evaporator container 510 (i.e., theamount of inerting fuel 508) can be controlled by an evaporatorcontainer valve 512, such as a float valve, and/or operation and/orcontrol by a controller 544. Rather than vaporizing the inerting fuel508 prior to supplying it into a catalytic reactor 522, the inertingfuel 508 can be vaporized and injected using an injector pump 566 thatis also used to mix the vaporized inerting fuel 508 (a first catalyst)with a second reactant provided from a second reactant source 520. Thefirst and second reactants are reacted within the catalytic reactor 522to generate an inert gas for supply into one or more fuel tanks (e.g.,fuel tank 502). Similar to the prior embodiment, a cool air source 528,such as ram air, is provided to enable cooling of the catalytic reactor522 as well as enable a condensing function within a heat exchanger 532,as described above. The heat exchanger 532 operates as a condenser on acatalyzed mixture to separate out an inert gas and a byproduct, asdescribed above. Because the inerting fuel 508 is vaporized as it passesthrough the injector pump 566, there is no need for a heater to beinstalled within or to the evaporator container 510. That is, theinerting fuel 508 is directly injected into the second reactant togenerate the composition to be reacted within the catalytic reactor 522.

In some embodiments, the injector pump 566 includes two or more separateelements that provide specific functions. For example, as shown in FIG.5, the injector pump 566 includes a pump 566 a that is arranged to pumpthe inerting fuel 508 to a high pressure and an injector/mixer 566 bthat is arranged to inject the inerting fuel 508 into the air streamsourced from the second reactant source 520.

Turning now to FIGS. 6A-6B, an embodiment of an inerting system 600 inaccordance with the present disclosure is shown. The inerting system 600may be similar to that shown and described above, and thus similarfeatures may not be shown or discussed for simplicity. The inertingsystem 600 enables the elimination of the heater that is used tovaporize the inerting fuel that is within an evaporator container.

As shown, the inerting system 600 includes a fuel tank 602 having fuel604 therein, with an ullage space 606 formed as fuel 664 is consumedduring use. In contrast to the above described embodiments, an inertingsupply line 654 fluidly connects the fuel tank 602 directly to acatalytic reactor 622. In this embodiment, a fuel-pump assembly 668 isinstalled within or along the inerting supply line 654 which is used tovaporize and mix inerting fuel (from the fuel 604) with a secondreactant from a second reactant source 620, with the mixture supplied toa catalytic reactor 622 for catalyzing. The operation of the fuel-pumpassembly 668 can be controlled by a controller 644.

FIG. 6B illustrates schematic details of the fuel-pump assembly 668. Asshown, fuel from the fuel tank 602 pumped using a fuel pump 668 a whichinjects fuel into a high pressure air supply nozzle 668 b. The highpressure air supply nozzle 668 b will vaporize the fuel 604 which isthen mixed with a second reactant supplied from the second reactantsource 620 within a mixing chamber 668 c. The mixture is then providedto the catalytic reactor 622. In the configuration shown in FIG. 6B,some amount of air from the second reactant source 620 will be suppliedto the high pressure air supply nozzle 668 b, as schematically shown.

It will be appreciated that FIG. 6B is merely illustrative, and it notto be limiting. Those of skill in the art will appreciate that theillustrative arrangement shown in FIG. 6B is an example, and otherarrangements and/or configurations are possible without departing fromthe scope of the present disclosure. For example, single-stagepumps/injectors can be used, where all the fuel (first source) issprayed directed into all of the air (second source) in a single step.

Turning now to FIG. 7, an embodiment of an inerting system 700 inaccordance with the present disclosure is shown. The inerting system 700may be similar to that shown and described above, and thus similarfeatures may not be shown or discussed for simplicity. The inertingsystem 700 enables the elimination of the heater that is used tovaporize the inerting fuel that is within an evaporator container.

As shown, the inerting system 700 includes a fuel tank 702 having fuel704 therein, with an ullage space 706 formed as fuel 704 is consumedduring use. An inerting supply line 754 fluidly connects the fuel tank702 to an evaporator container 710, as described above. The amount offuel 704 that is extracted into the evaporator container 710 (i.e., theamount of inerting fuel 708) can be controlled by an evaporatorcontainer valve, such as a float valve, and/or operation and/or controlby a controller 744. The inerting fuel 708 is vaporized within theevaporator container 710 to generate a first reactant for use within acatalytic reactor 722. A second reactant can be sourced from a secondreactant source 720, as described above. The first and second reactantsare reacted within the catalytic reactor 722 to generate an inert gasfor supply into one or more fuel tanks (e.g., fuel tank 702).

In this embodiment, to provide thermal energy for evaporation of theinerting fuel 708, rather than employing a heater element or device, thethermal energy can be supplied from the second reactant source 720. Thatis, relatively warm air (such as bleed air from a turbine engine) can bedirected into and/or through the evaporator container 710 through aheating duct 770. The heating duct 770 can pass through an interior ofthe evaporator container 710, may be wrapped around the evaporatorcontainer 710, and/or may have another arrangement such that thermalenergy within heating duct 770 can be transferred into the inerting fuel708 to thus vaporize the inerting fuel 708.

Although heating is provided into the inerting fuel to generate thefirst reactant (e.g., vaporization of fuel), the catalyst of the systemis exothermic and thus generates heat. Accordingly, it may be desirableto control temperatures such that the system does not over heat and/orsuch that an efficient temperature for catalyzation of the first andsecond reactants can be maintained within the catalyst. To achieve suchtemperature control, various systems are provided herein.

Turning now to FIG. 8, an embodiment of an inerting system 800 inaccordance with the present disclosure is shown. The inerting system 800may be similar to that shown and described above, and thus similarfeatures may not be shown or discussed for simplicity. The inertingsystem 800 employs various sources of air for cooling one or both of acatalytic reactor 822 and/or a heat exchanger 832. That is, a cool airsource 828 can replace the typical ram air source.

As shown, the inerting system 800 includes a fuel tank 802 having fuel804 therein, with an ullage space 806 formed as fuel 804 is consumedduring use. An inerting supply line fluidly connects the fuel tank 802to an evaporator container 810, as described above. The amount of fuel804 that is extracted into the evaporator container 810 (i.e., theamount of inerting fuel 808) can be controlled by an evaporatorcontainer valve and/or operation and/or control by a controller 844. Inthis illustrative embodiment, the inerting fuel 808 is vaporized using aheater 814 to generate a first reactant. A second reactant is sourcedfrom a second reactant source 820, and the first and second reactantsare mixed. The mixed first and second reactants are reacted within thecatalytic reactor 822 to generate an inert gas for supply into one ormore fuel tanks (e.g., fuel tank 802). The reactions that take placewithin the catalytic reactor 822 generates heat, with hot catalyzedproduct flowing into the heat exchanger 832. As noted above, cooling forthe catalytic reactor 822 and/or the heat exchanger 832 (e.g., for coolair supply and thermal transfer) is typically ram air.

In the present embodiment, the cool air source 828 is not ram air, butrather is sourced from another location on the aircraft. For example, insome embodiments, the cool air source 828 may be discharge from anenvironmental control system of the aircraft. Using outlet air from anenvironmental control system may enable condensing more water out of theinert gas stream and prevent such moisture from flowing into to the fueltank 802. In another embodiment, the cool air source 828 may bedischarge from a cabin of the aircraft. In such embodiments, the use ofcabin air can reduce ram air bleed, and thus reduce aircraft drag. Ineither arrangement, the cool air source 828 is provided to enablecooling of the catalytic reactor 822 as well as enable a condensingfunction within a heat exchanger 832, as described above. The heatexchanger 832 operates as a condenser on a catalyzed mixture to separateout an inert gas and a byproduct, as described above.

Another way of controlling temperatures within the fuel inerting systemsis to rearrange the catalyst and heat exchanger arrangement. Forexample, turning now to turning now to FIG. 9, an embodiment of aninerting system 900 in accordance with the present disclosure is shown.The inerting system 900 may be similar to that shown and describedabove, and thus similar features may not be shown or discussed forsimplicity. The inerting system 900 employs a modified arrangement of acatalytic reactor 922 and a heat exchanger 932. In this embodiment, acool air source 928 can be a typical ram air source arrangement.

As shown, the inerting system 900 includes a fuel tank 902 having fuel904 therein, with an ullage space 906 formed as fuel 904 is consumedduring use. An inerting supply line fluidly connects the fuel tank 902to an evaporator container 910, as described above. The amount of fuel904 that is extracted into the evaporator container 910 (i.e., theamount of inerting fuel 908) can be controlled by an evaporatorcontainer valve and/or operation and/or control by a controller 944. Inthis illustrative embodiment, the inerting fuel 908 is vaporized using aheater 914 to generate a first reactant. A second reactant is sourcedfrom a second reactant source 920, and the first and second reactantsare mixed. The mixed first and second reactants are reacted within thecatalytic reactor 922 to generate an inert gas for supply into one ormore fuel tanks (e.g., fuel tank 902). Water vapor may be condensed outof the catalyzed gas by passing through a heat exchanger 932, similar tothat described above.

However, in the present embodiment, rather than the catalyst beingadjacent to the heat exchanger such that both components may be suppliedwith cooling air next to each, the catalytic reactor 922 is arrangeddownstream from the heat exchanger 932. As such, a cooling flow from thecool air source 928 may provide a coolest air to the heat exchanger 932and a slightly warmer air may extend the heat exchanger 932 to enter thecatalytic reactor 922 and enable temperature control within thecatalytic reactor 922. Typically, using a catalyst cooled by ram air toinert a fuel tank, during cruise operation, the ram air flow needs to bereduced so significantly that the temperature of the air coming out ofthe cold side outlet of the catalyst can be excessive. In thearrangement shown in FIG. 9, the airflow through the ram circuit can beincreased such that the exhaust of the cold side of the catalyticreactor 922 (after passing through the heat exchanger 932) can bemaintained below 450° F.

Turning now to FIG. 10, an embodiment of an inerting system 1000 inaccordance with the present disclosure is shown. The inerting system1000 may be similar to that shown and described above, and thus similarfeatures may not be shown or discussed for simplicity. In thisembodiment, the inerting system 1000 employs ambient air as a secondreactant source 1020 as compared to the typical bleed air source used inseveral of the above described arrangements. Bleed air can supplypressurized air and oxygen into the inerting system 1000. However, itmay be advantageous to reduce or eliminate the amount of bleed air inaircraft systems, as such reductions can increase fuel efficienciesand/or reduce the need to install ducting within the aircraft to supplybleed air to the fuel inerting system.

As shown, the inerting system 1000 includes a fuel tank 1002 having fuel1004 therein, with an ullage space 1006 formed as fuel 1004 is consumedduring use. An inerting supply line fluidly connects the fuel tank 1002to an evaporator container 1010, as described above. The amount of fuel1004 that is extracted into the evaporator container 1010 (i.e., theamount of inerting fuel 1008) can be controlled by an evaporatorcontainer valve and/or operation and/or control by a controller 1044. Inthis illustrative embodiment, the inerting fuel 1008 is vaporized usinga heater 1014 to generate a first reactant. A second reactant is sourcedfrom a second reactant source 1020, which in this embodiment is ambientair. The first and second reactants are mixed and then reacted within acatalytic reactor 1022 to generate an inert gas for supply into one ormore fuel tanks (e.g., fuel tank 1002). In the present embodiment, thesecond reactant source 1020 is not bleed air, but rather is sourced fromthe ambient air outside of the aircraft. In this arrangement, a bloweror fan 1072 is arranged in or along a flow line of the second reactantsource 1020 and ambient air can be drawn through the system, thuseliminating the use of bleed air.

Turning now to FIG. 11, an arrangement of an inerting system 1100 inaccordance with an embodiment of the present disclosure is shown. Theinerting system 1100 may be similar to that shown and described above,and thus similar features may not be shown or discussed for simplicity.In this embodiment, the inerting system 1100 employs a back pressureflow restrictor 1174 positioned within or along a fuel tank supply line1156 downstream of a catalytic reactor 1122.

As shown, the inerting system 1100 includes a fuel tank 1102 having fuel1104 therein, with an ullage space 1106 formed as fuel 1104 is consumedduring use. An inerting supply line 1154 fluidly connects the fuel tank1102 to supply inerting fuel and/or a first reactant to the catalyticreactor 1122. As shown, in this embodiment, a fuel-pump assembly 1168(e.g., similar to that shown and described in FIGS. 6A-6B) is installedwithin or along the inerting supply line 1154. A second reactant from asecond reactant source 1120, with a mixture of the first and secondreactants supplied to the catalytic reactor 1122 for catalyzing. Theoperation of the fuel-pump assembly 1168 can be controlled by acontroller 1144.

For condensation and removal of water vapor, the minimum condensertemperature within a heat exchanger 1132 would be slightly abovefreezing. For condensation at atmospheric pressure, this temperaturewould result in approximately 0.6% mole fraction of water vapor in thesaturated gas stream exiting the heat exchanger 1132, because the H₂Osaturation vapor pressure at a temperature just above freezing isapproximately 0.6 kPa (and atmospheric pressure is approximately 100kPa). Because the H₂O saturation vapor pressure is only a function oftemperature (and not of total pressure), at higher total pressure themole fraction of water vapor becomes smaller, i.e., the gas streamexiting the heat exchanger 1132 becomes drier. For example, at 10 atmpressure (approximately 1000 kPa) the mole fraction of water vapor inthe saturated gas stream exiting the heat exchanger 1132 would beapproximately 0.06%. Thus, higher pressure operation is advantageous inkeeping the fuel system dry, because a drier gas stream would besupplied to the ullage space 1106 in the fuel tank 1102. In addition,operation of the catalytic reactor 1122 and heat exchanger 1132 athigher pressure would reduce the size required for these componentsbecause the working fluid (gas) would become more dense, and becauseheat transfer rates per unit surface area would increase with pressure(increase with working fluid density and Reynolds number).

The embodiment of FIG. 11 enables operation of the inerting system 1100at higher pressures than a pressure within the fuel tank 1102. Theincreased pressure can enable reducing the required size of thecatalytic reactor 1122 and/or heat exchanger 1132 and also provide adrier inert gas stream that is returned to the fuel tank 1102. Tooperate at higher pressures, liquid fuel from the fuel tank 1102 ispumped to higher pressure for delivery to the catalytic reactor 1122 bythe fuel-pump assembly 1168, and a high-pressure second reactant source1120, such as from an aircraft engine, is provided for catalyticoxidation of the fuel. The back pressure flow restrictor 1174 isprovided to regulate the operating pressure of the inerting system 1100,particularly at the catalytic reactor 1122 and the heat exchanger 1132.The back pressure flow restrictor 1174 can be configured to be activelycontrolled by the controller 1144 or may be a passive valve. In someembodiments, the back pressure flow restrictor 1174 may be a throttlingvalve, an electronic control valve (e.g., pneumatic control withfeedback), a passive orifice or restriction in the flow line, amechanical valve, or other type of flow restrictor, as will beappreciated by those of skill in the art. In some embodiments,controlled back pressure flow restrictors can be controlled in responseto operating conditions of the aircraft.

The back pressure flow restrictor 1174 is arranged to maintainhigh-pressure operation of the catalytic reactor 1122 and the heatexchanger 1132. The increased pressure provided by the back pressureflow restrictor 1174 enables more efficient water removal from theinerting system 1100. As shown, the back pressure flow restrictor 1174is located downstream of the catalytic reactor 1122 and the heatexchanger 1132, and in this embodiment, downstream of a water separator1138, although in some embodiments, the water separator 1138 can beomitted. Further, in some embodiments that include a water separator,the back pressure valve can be positioned downstream from the catalyticreactor 1122 and the heat exchanger 1132 but upstream of the waterseparator 1138.

Turning now to FIG. 12, an arrangement of an inerting system 1200 inaccordance with an embodiment of the present disclosure is shown. Theinerting system 1200 may be similar to that shown and described above,and thus similar features may not be shown or discussed for simplicity.In this embodiment, the inerting system 1200 employs an inert gasrecycling system 1276 positioned within or along a fuel tank supply line1256 downstream of a catalytic reactor 1222. As schematically shown inFIG. 12, the catalytic reactor 1222 has a different form factor than theother embodiments shown and described herein. For example, as shown, thecatalytic reactor is a simple monolith structure.

As shown, the inerting system 1200 includes a fuel tank 1202 having fuel1204 therein, with an ullage space 1206 formed as fuel 1204 is consumedduring use. An inerting supply line 1254 fluidly connects the fuel tank1202 to supply inerting fuel and/or a first reactant to the catalyticreactor 1222. As described above, the reaction between the first andsecond reactants (e.g., air and fuel) in the catalytic reactor 1222returns an inert gas to the fuel tank 1202 (with or without watercondensation and removal). Ideally, the gas stream returned to the fueltank 1202 would have zero or minimal O₂ (for maximum inerting effect),which would require near-stoichiometric reaction between the firstreactant (e.g., fuel) and the second reactant (e.g., air).

Unfortunately, reaction of fuel at near-stoichiometric conditions canresult in significant heat release and overheating of the catalyticreactor 1222. In some embodiments, to prevent such overheating, aportion of the product stream exiting the catalytic reactor 1222 can becooled and mixed with the first and second reactants before reaction atthe catalytic reactor 1222. That is, the recycling system 1276 cansupply a recycled product stream to the mixing of the first and secondreactants, upstream of the catalytic reactor 1222. In some embodiments,the recycled product can have the same composition as the gas exitingthe catalytic reactor 1222. In other embodiments, the recycled productsupplied through the recycling system 1276 can have a differentcomposition if the water is first condensed and removed (separated) fromthe exiting gas. Further, in some embodiments, if the water is condensedand separated, either the water itself can be recycled to the catalyticreactor 1222, or the gas stream without water (e.g., containing CO₂ andN₂) can be recycled to the catalytic reactor 1222.

Although shown in FIG. 12 with the recycling system 1276 locateddownstream or after a water separator 1238, in some embodiments, thewater separator can be located downstream of the recycling system. Thatis, in some embodiments, a water separator can be placed in the lineleading to the fuel tank, but after the extraction of the recyclestream. Those of skill in the art will appreciate that the location ofan extraction point for the recycling system can be located anyway alonga fluid line of the systems described herein. Such arrangement can allowwater to be recycled to the catalyst (to help with catalyst cooling),and allow removal of water before delivery of dry inert-gas (or drylow-oxygen gas) to the fuel tank ullage. Further, in some embodiments,regardless of where the water is removed from the line, some portion ofthe extracted water can be added to the recycle stream (or directlydelivered to the catalyst) to help keep the catalyst cool.

Regardless of the source or composition of the recycled product,operation of the catalytic reactor 1222 at a safe temperature while fueland air are catalytically reacted at near-stoichiometric conditions isachievable. For example, by cooling and recycling a portion of theproduct stream to act as a diluent during reaction, the temperature riseassociated with reaction of fuel with air can be reduced. In addition,if desired, the recycled product stream (e.g., cool diluent) can be usedas a sparge gas to deliver fuel vapor to the catalyst.

For example, turning now to FIG. 13, an arrangement of an inertingsystem 1300 in accordance with an embodiment of the present disclosureis shown. The inerting system 1300 may be similar to that shown anddescribed above, and thus similar features may not be shown or discussedfor simplicity. In this embodiment, the inerting system 1300 employs aninert gas recycling system 1376 positioned within or along a fuel tanksupply line 1356 downstream of a catalytic reactor 1322, but may supplythe recycled product stream to an evaporator container 1310.

As shown, the inerting system 1300 includes a fuel tank 1302 having fuel1304 therein, with an ullage space 1306 formed as fuel 1304 is consumedduring use. An inerting supply line 1354 fluidly connects the fuel tank1302 to the evaporator container 1310 to generate an inerting fueland/or a first reactant to be supplied to a catalytic reactor 1322. Asdescribed above, the reaction between the first and second reactants(e.g., air and fuel) in the catalytic reactor 1322 returns an inert gasto the fuel tank 1302 (with or without water condensation and removal).

Similar to the embodiment shown in FIG. 12, the inerting system 1300includes a recycling system 1376. In this case, the recycling system1376 diverts a portion of the product stream exiting the catalyticreactor 1322 from the fuel tank supply line 1356. The extracted productis supplied into the evaporator container 1310. As shown, a return line1378 can be arranged to cycle a portion of the fuel within theevaporator container 1310 back to the fuel tank 1302. In thisembodiment, the recycled gas would flow through the recycling system1376 and into the evaporator container 1310 to perform sparging. Assuch, the recycled gas would accrue fuel vapor to formed sparge-gas anda sparge-gas/fuel-vapor mixture would then be mixed with air anddelivered to the catalytic reactor 1322.

Although shown herein with the recycle stream being purely directed toand passing through the sparger (i.e., evaporator container 1310), thepresent disclosure is not so limited. For example, in some non-limitingembodiments, a portion of the recycle stream is directed to pass throughthe sparger and the remainder of the recycle stream is sent directly tothe catalyst (i.e., bypassing the sparger and feeding directly into thecatalytic reactor 1322). That is, in some embodiments, two recycle linescan be employed that combine the arrangements shown in FIGS. 12-13. Insuch embodiments, by allowing only a fraction of the recycle stream topass through the sparger, the sparger flowrate can be adjusted asneeded, independently of the recycle flow rate.

In either of the embodiments shown in FIGS. 12-13, a recycled product(e.g., an inert gas) is recycled to the inlet of the catalytic reactor.The inert gas can act as a heat absorber and have no reaction within thecatalytic reactor. Because the recycled product will not react with thecatalytic reactor (i.e., no chemical reaction) no heat will be generatedby this portion of the gas flowing into and through the catalyticreactor. Accordingly, the fuel-air mixture of the first and secondreactants will be diluted, which will thus lower the temperature withinthe catalytic reactor.

In some embodiments, the recycling systems 1276, 1376 can include pumpsor blowers arranged to force a portion of the product stream backupstream of the respective catalytic reactor 1222, 1322. Further, one ormore valves may be part of the recycling systems 1276, 1376 to control avolume of the bled off product from the fuel tank supply line 1256,1356. In some embodiments, an ejector pump or an injector pump can belocated upstream of the catalytic reactor with a flow line connecteddownstream from the catalytic reactor, with the ejector pump or injectorpump drawing the product back to an upstream position. In someembodiments, a blower can be arranged downstream of the catalyticreactor with the blower arranged to draw off and blow a portion of theproduct stream back to upstream of the catalytic reactor. In someembodiments, a controller can be arranged to control an amount ofproduct stream that is recycled as compared to an amount that issupplied into the ullage, as described above.

The recycling systems provided herein can be arranged to recycle anygiven or predetermined ratio or percentage. For example, in anon-limiting example, fifty-parts of the reacted product stream may berecycled for every one-part that is supplied into the ullage. This ismerely an example, and in some embodiments, as much as 99% of thereacted product stream can be recycled, with only 1% being supplied intothe ullage. In contrast, at the other extreme, a very low percentage,such as 5% or lower of the reacted product stream can be recycled, with95% or more of the reacted product stream being supplied into theullage.

Turning now to FIG. 14, an arrangement of an inerting system 1400 inaccordance with an embodiment of the present disclosure is shown. Theinerting system 1400 may be similar to that shown and described above,and thus similar features may not be shown or discussed for simplicity.In this embodiment, the inerting system 1400 employs a fuel vaporizationsystem 1480. The fuel vaporization system 1480 is arranged to transferfuel 1404 from an aircraft fuel tank 1402 into a container 1482, whichis arranged to perform sparging. The fuel 1404 is metered into thecontainer 1482 by a container valve 1412. Air is introduced from an airsource 1484 to a location below the fuel level within the container1482. The introduction of the air into the fuel may be through a nozzleor frit 1486 located within the container 1482. The air will passthrough the fuel as air bubbles and fuel vapor will evaporate into theair bubbles. The combined fuel-and-air bubbles will be deposited in avapor space 1488 above the fuel level in the container 1482, thusforming a vaporized fuel-air mixture in the vapor space 1488. In someembodiments, the fuel-air mixture can be set by the temperature of theair entering the container 1482 from the air source 1484 and/orcontrolled by the design of the nozzle or frit 1486. The fuel-airmixture within the vapor space 1488 can be then used to feed a catalyticreactor 1422. Further, as shown schematically, in some embodiments, aportion of the air from the air source 1484 can be directed to mixdownstream of the vapor space 1488, prior to introduction (e.g.,injection) into the catalytic reactor 1422. Downstream of the catalyticreactor 1422, the inerting system 1400 may be substantially similar toone or more of the embodiments described above.

In some of the above described embodiments, restrictions associated withtemperatures may be present. For example, a minimum inlet temperature tothe catalyst for light-off and a maximum outlet temperature for hardwarelocated in a fuel vapor zone may be imposed. In some embodiments,recirculation of catalyst discharge gas may be employed to ensurecompliance with such restrictions. However, the temperature of thatrecirculated gas must not exceed the temperature limit of an electricmotor-driven fan.

In some embodiments, air is recirculated back to the catalyst inlet at aratio of ˜20:1 in order for the temperature upstream to the catalyst isgreater than or equal to a light-off temperature while maintaining acatalyst outlet temperature to be less than an auto-ignition temperature(e.g., approximately 450° F.). In accordance with some embodiments, anelectric motor-driven fan may be employed to achieve desiredrecirculation ratios. However, an inlet temperature of a conventionaloil bearing fan may be limited to approximately 200° F. Moreover, atemperature of the air leaving a heat exchanger may be required to beapproximately 60° F. to condense water and remove such water using awater collector, as described above.

In accordance with some embodiments, a reheater/condenser combination(hot side) may be sized to achieve a temperature of about 60° F.Further, a reheater cold side may be sized to warm fan discharge airback up to achieve light off temperature.

Turning now to FIG. 15, an arrangement of an inerting system 1500 inaccordance with an embodiment of the present disclosure is shown. Theinerting system 1500 may be similar to that shown and described above,and thus similar features may not be shown or discussed for simplicity.In this embodiment, the inerting system 1500 includes a catalyticreactor 1522 located upstream of a heat exchanger 1524, similar to thatshown and described above. Inert gas can be generated within thecatalytic reactor 1522 and the heat exchanger 1524 may cool the gas toenable extraction of water prior to supplying the inert gas back to afuel tank.

In this embodiment, thermal control can be achieved throughrecirculating air from the output of the heat exchanger 1524 andinjecting the air back into an airstream upstream of the catalyticreactor 1522. A recirculation loop 1590 is arranged to fluidly extendfrom a hot corner tap 1592 on the heat exchanger 1524 to a locationupstream of the catalytic reactor 1522. The hot corner tap 1592 is aportion of the outlet of the heat exchanger 1524 having the highest heatcontent. For example, in one non-limiting embodiment, the bulk averagetemperature of the output of the air from the heat exchanger 1524 isapproximately 60° F. The heat exchanger 1524 has a hot corner withtemperatures greater than 60° F. and a cold corner with temperaturesless than 60° F. The hot corner is the portion of the heat exchanger1524 that is farthest from the cold air cross flowing from a cool airsource 1528 (e.g., ram air). The cold corner of the heat exchanger 1524is the side of the heat exchanger 1524 closest to the cool air source(i.e., is the side contacted by the cool air first).

The recirculation loop 1590 includes a recirculation fan 1594 (e.g., anelectric motor-driven fan) and a reheater 1596. The recirculation fan1594 is arranged to cause a portion of the air at the outlet of the heatexchanger 1524 (e.g., at the hot corner tap) to be withdrawn andrecirculated back to the catalytic reactor 1522. The reheater 1596 isprovided and arranged to heat the air within the recirculation loop 1590to sufficient temperature to achieve desired air temperatures upstreamof the catalytic reactor 1522. In some embodiments, the reheater 1596 isarranged downstream of the catalytic reactor 1522 and upstream of theheat exchanger 1524, with the heated air exiting from the catalyticreactor 1522 serving as a heating element to warm the air within therecirculation loop 1590 prior to reinjection into the flow upstream ofthe catalytic reactor 1522.

The reheater 1596 performs two functions. Firstly, the reheater 1596 isarranged to heat the air that is pulled from the hot corner tap 1592 ofthe heat exchanger 1524. The heated air is then mixed with the fuel/airmixture prior to entry into the catalytic reactor 1522, thus raising thetemperature of the fuel/air mixture, thereby improving the reactionefficiency. Secondly, the reheater 1596 will cool the air that exitsfrom the catalytic reactor 1522 prior to such reacted air from enteringthe heat exchanger 1524, thereby improving the efficiency of the systemas a whole, including operation of the heat exchanger 1524 (e.g.,improved water extraction). Additionally, because the air exiting thecatalytic reactor 1522 is cooled twice, i.e., within the reheater 1596and then in the heat exchanger 1524, the air extracted at the hot cornertap 1592 may be sufficiently cool to ensure efficient operation of therecirculation fan 1594, which may have an upper thermal limit foroperation.

Also shown in FIG. 15, the inerting system 1500 may include an optionalfuel pump 1566. The fuel pump 1566 may be arranged similar to thefuel-pump assembly 668 shown in FIGS. 6A-6B. The fuel pump 1566 can bearranged to increase a flow rate and/or pressure within the system toensure an inert gas is supplied to a fuel tank and also to ensureoperation of the recirculation loop 1590.

Turning now to FIG. 16, an arrangement of an inerting system 1600 inaccordance with an embodiment of the present disclosure is shown. Theinerting system 1600 may be similar to that shown and described above,and thus similar features may not be shown or discussed for simplicity.The inerting system 1600 is similar to the inerting system 1500 shown inFIG. 15. The inerting system 1600 includes a catalytic reactor 1622located upstream of a heat exchanger 1624, with a reheater 1696 locatedtherebetween. Inert gas can be generated within the catalytic reactor1622 and the heat exchanger 1624 may cool the gas to enable extractionof water prior to supplying the inert gas back to a fuel tank.

In this embodiment, a recirculation loop 1690 does not pull from a hotcorner tap, but rather extracts air from downstream of the heatexchanger 1624 at recirculation junction 1698, which is located upstreamof a water collector. The recirculation loop 1690 includes arecirculation fan 1694 and flows through the reheater 1696, as describedabove. In this case, rather than pulling air from a hot corner tap(e.g., at greater than 60° F.), the air pulled into the recirculationloop 1690 may be about 60° F. (i.e., the bulk average of the air exitingthe heat exchanger 1624).

Turning now to FIG. 17, an arrangement of an inerting system 1700 inaccordance with an embodiment of the present disclosure is shown. Theinerting system 1700 may be similar to that shown and described above,and thus similar features may not be shown or discussed for simplicity.The inerting system 1700 is similar to the inerting systems 1500, 1600shown in FIGS. 15-16. The inerting system 1700 includes a catalyticreactor 1722 located upstream of a heat exchanger 1724, with a reheater1796 located therebetween. Inert gas can be generated within thecatalytic reactor 1722 and the heat exchanger 1724 may cool the gas toenable extraction of water prior to supplying the inert gas back to afuel tank.

In this embodiment, a recirculation heat exchanger 1799 is arrangedimmediately downstream of the catalytic reactor 1722 and reheater 1796,and upstream of the heat exchanger 1724 that is arranged as a condenserto extract and remove moisture from the output of the catalytic reactor1722. The recirculation loop 1790 includes a recirculation fan 1794 andflows through the reheater 1796, as described above. As shown, therecirculation heat exchanger 1799 is located downstream of the heatexchanger 1724 relative to a flow of cool air from a cool air source1728, and thus is farthest from the cold air cross flowing from the coolair source 1528 (e.g., ram air). The output of the recirculation heatexchanger 1799 may be divided such that a portion of the air flows intothe recirculation loop 1790 and a portion flows into the condenser heatexchanger 1724. The outlet air from the recirculation heat exchanger1799 may be about 200° F., and is pulled through the recirculation loop1790 by the recirculation fan 1794. The various sizes, shapes, andconfigurations of the recirculation heat exchanger 1799 and thecondenser heat exchanger 1724 may be selected to determine and set aflow pattern (e.g., amount of air sent through recirculation loop 1790and amount of air sent to the condenser heat exchanger 1724) and tocontrol temperatures of the air at various locations within the inertingsystem 1700,

The reheater in the above described embodiments is a regenerative heatexchanger that can passively reheat a portion of air prior to injectionor passing through the catalytic reactor. As discussed above, thetemperature of the air as it passes through the catalytic reactorimpacts the efficiency thereof. The reheater allows for improvedefficiencies through increasing an inlet temperature of the catalyticreactor and also reducing the outlet temperature of the air, prior tointroduction into a condensing heat exchanger.

Advantageously, embodiments of the present disclosure provide efficientmechanisms for generating inert gas and supplying such inert gas intofuel tanks of aircraft. Further, advantageously, embodiments providedherein can prevent ambient air (possibly containing water) from enteringan aircraft fuel tank. To prevent ambient air from entering the aircraftfuel tank, a controller of an inerting system as described herein, cansupply inert gas into the fuel tank to maintain a desired pressure(e.g., providing a higher pressure within the fuel tank than ambientpressures). Such increased pressure can be employed within the fuel tankto prevent ingress of oxygen-rich air (e.g., ambient air). This may beparticularly useful during a descent phase of flight of an aircraft asthe ambient pressures increase as the altitude decreases.

Further, advantageously, embodiments provided herein can improveoperation efficiency of catalytic reactor systems by controlling airtemperatures at various locations within the system. For example,embodiments described herein can enable increased temperatures upstreamof a catalytic reactor and decreased temperatures downstream of thecatalytic reactors and upstream of a condensing heat exchanger, ascompared to system that do not include recirculation loops, as describedherein. Such temperature control can improve efficiency of the catalyticreactor fuel inerting systems.

The use of the terms “a,” “an,” “the,” and similar references in thecontext of description (especially in the context of the followingclaims) are to be construed to cover both the singular and the plural,unless otherwise indicated herein or specifically contradicted bycontext. The modifier “about” and/or “approximately” used in connectionwith a quantity is inclusive of the stated value and has the meaningdictated by the context (e.g., it includes the degree of errorassociated with measurement of the particular quantity). All rangesdisclosed herein are inclusive of the endpoints, and the endpoints areindependently combinable with each other.

While the invention has been described in detail in connection with onlya limited number of embodiments, it should be readily understood thatthe invention is not limited to such disclosed embodiments. Rather, theinvention can be modified to incorporate any number of variations,alterations, substitutions, combinations, sub-combinations, orequivalent arrangements not heretofore described, but which arecommensurate with the spirit and scope of the invention. Additionally,while various embodiments of the invention have been described, it is tobe understood that aspects of the invention may include only some of thedescribed embodiments.

Accordingly, the present disclosure is not to be seen as limited by theforegoing description, but is only limited by the scope of the appendedclaims.

What is claimed is:
 1. A fuel tank inerting system for an aircraft, thesystem comprising: a fuel tank; a first reactant source fluidlyconnected to the fuel tank, the first source arranged to receive fuelfrom the fuel tank; a second reactant source; a catalytic reactorarranged to receive a first reactant from the first source and a secondreactant from the second source to generate an inert gas that issupplied to the fuel tank to fill a ullage space of the fuel tank; aheat exchanger arranged between the catalytic reactor and the fuel tankand configured to at least one of cool and condense an output from thecatalytic reactor to separate out an inert gas and a byproduct; areheater arranged between the catalytic reactor and the heat exchanger;and a recirculation loop configured to extract air from downstream ofthe heat exchanger, pass the extracted air through the reheater, andinject reheated air upstream of the catalytic reactor.
 2. The system ofclaim 1, further comprising a recirculation fan located within therecirculation loop, the recirculation fan configured to pull air fromdownstream of the heat exchanger.
 3. The system of claim 2, wherein therecirculation fan is an electric motor-driven fan.
 4. The system ofclaim 1, wherein the recirculation loop fluidly connects to the heatexchanger at a hot corner tap of the heat exchanger.
 5. The system ofclaim 1, wherein the recirculation loop fluidly connects downstream ofthe heat exchanger at a recirculation junction.
 6. The system of claim1, wherein the heat exchanger comprises a recirculation heat exchangerand a condenser heat exchanger, wherein output from the catalyticreactor passes through the reheater and into the recirculation heatexchanger and is subsequently divided to the recirculation loop and thecondenser heat exchanger.
 7. The system of claim 1, further comprising awater separator located between the catalytic reactor and the fuel tankand downstream of the catalytic reactor, the water separator arranged toextract water from the reacted first reactant and second reactant. 8.The system of claim 1, further comprising an injector pump arranged toreceive the first reactant and the second reactant and to supply amixture of the first reactant and the second reactant to the catalyticreactor.
 9. The system of claim 1, further comprising a fuel pumpconfigured to pump fuel from the fuel tank to the catalytic reactor. 10.The system of claim 1, wherein the byproduct is water.
 11. A method ofsupplying inert gas to a fuel tank of an aircraft, the methodcomprising: extracting fuel from a fuel tank as a first reactant source;mixing the first reactant with a second reactant supplied from a secondreactant source; catalyzing the mixed first reactant and second reactantwithin a catalytic reactor; cooling the catalyzed mixture of the firstand second reactants with a heat exchanger to produce an inert gas;supplying the inert gas to the fuel tank to fill a ullage space of thefuel tank; and recirculating and reheating, through a recirculationloop, a portion of the reacted first and second reactants and supplyingthe recirculated portion to a location upstream of the catalyticreactor, wherein a reheater is located between the catalytic reactor andthe heat exchanger.
 12. The method of claim 11, further comprisingpulling air from downstream of the heat exchanger using a recirculationfan located within the recirculation loop.
 13. The method of claim 12,wherein the recirculation fan is an electric motor-driven fan.
 14. Themethod of claim 11, wherein the recirculation loop fluidly connects tothe heat exchanger at a hot corner tap of the heat exchanger.
 15. Themethod of claim 11, wherein the recirculation loop fluidly connectsdownstream of the heat exchanger at a recirculation junction.
 16. Themethod of claim 11, wherein the heat exchanger comprises a recirculationheat exchanger and a condenser heat exchanger, wherein output from thecatalytic reactor passes through the reheater and into the recirculationheat exchanger and is subsequently divided to the recirculation loop andthe condenser heat exchanger.
 17. The method of claim 11, furthercomprising extracting water from the reacted first reactant and secondreactant using a water separator located between the catalytic reactorand the fuel tank and downstream of the catalytic reactor.
 18. Themethod of claim 11, further comprising mixing the first reactant and thesecond reactant using an injector pump and supplying the mixed firstreactant and second reactant to the catalytic reactor.
 19. The method ofclaim 11, further comprising pumping fuel from the fuel tank to thecatalytic reactor using a fuel pump.
 20. The method of claim 11, whereinthe extracted portion downstream of the heat exchanger and within therecirculation loop is between 60° F. and 200° F.